JP5370669B2 - 2-cycle engine - Google Patents

Description

  The present invention relates to a two-cycle engine.

  Conventionally, a two-cycle gasoline engine has been used as a power source for portable power working machines such as brush cutters and chainsaws. In this type of two-cycle engine, scavenging of the cylinder chamber is performed using an air-fuel mixture precompressed in the crank chamber. Specifically, the air-fuel mixture is sucked from the intake port into the crank chamber below the piston by the upward stroke of the piston, the air-fuel mixture is pre-compressed by the downward stroke of the piston, and the pre-compressed air-fuel mixture is discharged from the scavenging port. The combustion gas is discharged by blowing out into the cylinder chamber above the piston.

  In such a scavenging process of a two-cycle engine, when the fuel (gasoline) and air mixture (fresh air) is sent from the crank chamber to the cylinder chamber through the scavenging passage, the fresh gas is scavenged with fresh air. Phenomenon (blown through) easily discharged with combustion gas. When blow-through occurs, unburned fuel (gasoline) contained in fresh air is released into the atmosphere, resulting in an increase in fuel consumption rate and problems such as air pollution.

  In order to prevent or reduce blow-by, a stratified scavenging two-cycle engine is known (see, for example, Patent Documents 1 and 2). In the stratified scavenging type two-cycle engine, the scavenging passage is filled with air before the exhaust process, and the combustion gas is scavenged with air in the initial stage of the scavenging process, and is discharged together with the combustion gas. Replacing fresh air with air prevents or reduces unburned fuel from being released into the atmosphere.

International Publication No. 98/57053 International Publication No. 00/65209

  However, in a stratified scavenging two-cycle engine, air may remain locally in the combustion chamber to prevent ignition, and the combustion efficiency (output) may be lower than that in a two-cycle engine that scavenges with only the air-fuel mixture.

  In addition, since the stratified scavenging type two-cycle engine is intended to scavenge by sending a sufficient amount of air into the cylinder chamber, the concentration of the air-fuel mixture sucked from the air-fuel mixture intake port is reduced accordingly. It needs to be higher than a two-cycle engine. As a result, the stratified scavenging two-cycle engine makes it difficult to adjust the carburetor, and the sensitivity of the carburetor is meteorological conditions such as temperature, pressure, temperature, etc., load fluctuation of the work equipment (the two-cycle engine is installed) If the working machine is a brush cutter, it becomes sensitive to the grass hardness and quantity) and the habituation of the equipment (whether it is just after startup or after sufficient warm-up operation), which hinders the setting of optimal operating conditions. Had come. In particular, working machines such as brush cutters and chainsaws are required to maximize the output of the engine in various environments combined with environmental factors such as weather conditions and load fluctuations.

Further, in a stratified scavenging type two-cycle engine in which an air intake port and a scavenging port are connected by a communication passage provided in a piston, a communication passage of the piston that connects the air intake port and the scavenging port is provided in the cylinder chamber and the entire stroke of the piston. One of the problems is that the piston length becomes longer because it must be disconnected from the crankcase, and as a result, the engine becomes larger.

  On the other hand, it is also required to suppress the emission of unburned gasoline rather than a normal two-cycle engine that scavenges only with the air-fuel mixture.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a new scavenging type two-cycle engine that can suppress unburned fuel emission while suppressing the increase in size of the engine and that can maximize the output of the engine in a wide range of environments. It is to provide.

  To achieve the above object, a two-cycle engine according to the present invention is partitioned by a cylinder having an inner surface constituting a bore, a piston reciprocating in the bore of the cylinder, the inner surface of the cylinder and the piston. A cylinder chamber, a crank chamber configured on the lower side of the piston, an air-fuel mixture intake port for allowing a fuel-air mixture to flow into the crank chamber, and the cylinder through the scavenging passage. A scavenging port provided on the inner surface of the cylinder for flowing into the chamber, and an exhaust port provided on the inner surface of the cylinder for discharging combustion gas in the cylinder chamber, wherein the piston A communication passage that is open to the crank chamber, and further, the inside of the cylinder for allowing air to flow into the communication passage. After the outer surface of the piston moving from the bottom dead center to the top dead center closes the scavenging port with respect to the cylinder chamber, the communication path is connected to the air intake port and the air intake port. The communication passage is opened at the outer surface of the piston so as to communicate with the scavenging port, whereby the air flowing into the communication passage from the air intake port and the air-fuel mixture in the communication passage are more than the air-fuel mixture. The lean air-fuel mixture flows through the scavenging port into the scavenging passage, and the outer surface of the piston moving from the top dead center to the bottom dead center serves as the exhaust port and the scavenging air. When the port is opened to the cylinder chamber, the combustion gas is scavenged by the lean air-fuel mixture.

  In the two-cycle engine configured as described above, after the piston moves from the bottom dead center to the top dead center, the outer surface of the piston closes the scavenging port with respect to the cylinder chamber, and then enters the crank chamber. The open communication path communicates with the air intake port and the scavenging port. Thereby, the air flowing into the communication passage from the air intake port and the air-fuel mixture in the communication passage form a leaner air-fuel mixture than the air-fuel mixture, and this lean air-fuel mixture passes through the scavenging port. It flows into the scavenging passage. Then, when the piston opens the exhaust port and the scavenging port to the cylinder chamber while the piston moves from the top dead center to the bottom dead center, first, the lean air-fuel mixture in the scavenging passage The gas flows into the cylinder chamber and the combustion gas is scavenged by the lean air-fuel mixture.

  Even if the lean air-fuel mixture blows out from the exhaust port, since the air-fuel mixture is lean, discharge of unburned fuel is suppressed as compared with a normal two-cycle engine that scavenges only with the air-fuel mixture.

  Further, even if the lean air-fuel mixture remains locally in the cylinder chamber (as a result, the combustion chamber), the lean air-fuel mixture containing fuel does not hinder ignition, so that the air layer containing no fuel Unlike the case where it remains locally in the combustion chamber, the air-fuel mixture in the combustion chamber is reliably ignited and combustion is performed.

In addition, since the air and air-fuel mixture sucked from the air intake port are mixed and sent to the cylinder chamber as the lean air-fuel mixture, the concentration of the air-fuel mixture sucked from the air-fuel mixture intake port is extremely increased. Therefore, the carburetor can be adjusted stably even when the environmental factors change.

  Further, since the communication passage of the piston is opened to the crank chamber, the piston length can be shortened as compared with a stratified scavenging two-cycle engine, and as a result, the engine is increased in size. Can be suppressed.

  In an embodiment of the present invention, the outer surface of the piston moving from bottom dead center to top dead center is after the scavenging port is closed with respect to the cylinder chamber, and the mixture intake port is with respect to the crank chamber. The communication path may be opened at the outer surface of the piston so that the communication path communicates with the air intake port and the scavenging port for a certain period before being opened.

  In an embodiment of the present invention, it is preferable that the communication path remains in communication with the scavenging port for a period from when the communication with the air intake port is started to the end with at least the outer surface of the piston. is there.

  In the embodiment configured as described above, a lean air-fuel mixture formed by the air flowing into the communication passage from the air intake port and the air-fuel mixture in the communication passage is efficiently supplied to the scavenging passage through the scavenging port. And a sufficient amount of lean air-fuel mixture can be introduced into the scavenging passage.

  In the embodiment of the present invention, the communication path includes a first port that is formed inside the piston and opens to the scavenging port, and a second port that opens to the air intake port. Alternatively, the communication path may be a groove formed on the outer surface of the piston.

  In the embodiment of the present invention, preferably, the air-fuel mixture intake port is provided on the inner surface of the cylinder, and is opened and closed with respect to the crank chamber by the outer surface of the piston.

  In the embodiment configured as described above, the structure of the scavenging two-cycle engine described above can be simplified.

  As described above, the new scavenging type two-cycle engine according to the present invention suppresses the increase in size of the engine and suppresses the discharge of unburned fuel as compared with a normal two-cycle engine that scavenges only with the air-fuel mixture. In addition, the engine output can be maximized in a wide range of environments.

1 is a cross-sectional view of a two-cycle engine according to the present invention when a piston is at bottom dead center. It is sectional drawing in line II-II of FIG. 1 which abbreviate | omitted the piston. It is sectional drawing in line III-III of FIG. FIG. 4 is a cross-sectional view taken along line IV-IV in FIG. 3 when the piston is above the position shown in FIG. 1. FIG. 5 is a cross-sectional view similar to FIG. 1 when the piston is above the position shown in FIG. 4. It is sectional drawing similar to FIG. 1 when a piston exists in a top dead center.

  Embodiments of a two-cycle engine according to the present invention will be described below with reference to the drawings. FIG. 1 is a cross-sectional view of a two-cycle engine according to the present invention when the piston is at bottom dead center. 2 is a cross-sectional view taken along line II-II in FIG. 1 with the piston omitted. 3 is a cross-sectional view taken along line III-III in FIG.

  As shown in FIG. 1, a two-cycle engine 1 according to an embodiment of the present invention is a gasoline engine, has a cylinder 2 having an inner surface 2a constituting a bore 8a, an inner surface 4a, and is connected to the cylinder 2. And a piston 6 that reciprocates in the bore 8 a of the cylinder 2.

  The two-cycle engine 1 has a cylinder chamber 8 partitioned by the inner surface 2 a of the cylinder 2 and the piston 6, and a crank chamber 10 partitioned by the inner surface 4 a of the crankcase 4 and the piston 6. . The crank chamber 10 is configured on the lower side of the piston 6. The piston 6 is connected to the crankshaft 14 via a pin 12 and a connecting rod 13 and reciprocates between a top dead center (see FIG. 6) and a bottom dead center (see FIG. 1). When the piston 6 reciprocates, the volume of the cylinder chamber 8 and the volume of the crank chamber 10 increase or decrease.

  The inner surface 2a of the cylinder 2 also forms a combustion chamber 8b on the bore 8a, and a spark plug 15 is disposed in the combustion chamber 8b.

  As shown in FIGS. 1 to 3, the two-cycle engine 1 includes a mixture intake port 18 through which a mixture of fuel and air flows into the crank chamber 10, and a scavenging passage for the mixture in the crank chamber 10. A scavenging port 22 provided on the inner surface 2 a of the cylinder 2 for flowing into the cylinder chamber 8 through 20, and an inner surface 2 a of the cylinder 2 for discharging combustion gas in the cylinder chamber 2. And an exhaust port 24.

  A mixture passage 18a extends from the mixture intake port 18 toward a carburetor (not shown). In the present embodiment, the air-fuel mixture intake port 18 is provided on the inner surface 2 a of the cylinder 2 and is opened and closed with respect to the crank chamber 10 by the outer surface 6 a of the piston 6. The air-fuel mixture intake port 18 opens into the cylinder chamber 8 when the piston 6 is at least at the top dead center (see FIG. 6).

  An exhaust passage 24a extends from the exhaust port 24 toward an exhaust port (not shown). The exhaust port 24 is opened and closed with respect to the cylinder chamber 8 by the outer surface 6 a of the piston 6. The exhaust port 24 opens into the cylinder chamber 8 when the piston 6 is at least at the bottom dead center (see FIG. 1). As shown in FIG. 3, the exhaust port 24 is provided at a position shifted by about 180 degrees with respect to the air-fuel mixture intake port.

  As shown in FIG. 3, two scavenging ports 22 are provided at positions shifted by about 90 degrees in both directions with respect to the air-fuel mixture intake port 18. The scavenging passage 20 extending from each of the scavenging ports 22 terminates at a port 26 that opens into the crank chamber 10 through the inside of the cylinder 2. The scavenging port 22 is opened and closed with respect to the cylinder chamber 8 by the outer surface 6 a of the piston 6. The scavenging port 22 opens into the cylinder chamber 8 when the piston 6 is located at least at the bottom dead center (see FIG. 1).

  In the present embodiment, the exhaust port 24 and the scavenging port 22 have a substantially rectangular shape, and their upper end face positions are substantially the same. The air-fuel mixture intake port 18 is located below the exhaust port 24 and the scavenging port 22.

  Further, the two-cycle engine 1 has an air intake port 30 provided on the inner surface 2a of the cylinder 2 in order to allow air to flow into the communication passage 28 (which will be described in detail later) of the piston 6. Yes. As shown in FIG. 3, one air supply port 30 is provided on each side of the air-fuel mixture intake port 18. An air passage 30a extends from each of the air intake ports 30 toward an air supply unit (not shown). The air intake port 30 is opened and closed with respect to the communication path 28 by the outer surface 6 a of the piston 6. The air supply port 30 is disposed above the air-fuel mixture intake port 18 and is located below the exhaust port 24 and the scavenging port 22.

  The pin 12, which is pivotally connected to the piston 6, extends in a direction substantially perpendicular to a line connecting the exhaust port 24 and the air-fuel mixture intake port 18. The piston 6 has the communication passage 28 having an opening 32 for the crank chamber 10. Two communication passages 28 are provided corresponding to the air intake ports 30. Each of the communication passages 28 is opened at the outer surface 6 a of the piston 6 so as to communicate with the air intake port 30 and the scavenging port 22. In the present embodiment, the communication passage 28 is formed inside the piston 6 and has a first port 34 that opens to the scavenging port 22 and a second port 36 that opens to the air intake port 30. ing.

  The communication passage 28 is configured such that air flowing in from the air intake port 30 and the second port 36 is directed to the first port 34 and the scavenging port 22 while flowing in the communication passage 28. It is configured. The first port 34 is recessed from the outer surface 6 a of the piston 6 at a portion overlapping the pin 12, thereby communicating with the two scavenging ports 22.

  The first port 34 is disposed above the second port 36. The vertical opening length of the second port 36 is preferably substantially equal to the vertical opening length of the air intake port 30. When the second port 36 and the air intake port 30 are aligned with each other, the first port 34 is aligned with the scavenging port 22. The opening length in the vertical direction of the first port 34 is larger than the opening length in the vertical direction of the second port 36. The vertical length of the first port 34 is such that the air intake port 30 and the second port 36 of the communication passage 28 communicate with each other at least during the movement of the piston 6 from the bottom dead center to the top dead center. It is preferable that the first port 34 of the communication passage 28 and the scavenging port 22 remain in communication during a period from the start to the closing.

  Next, the operation of the two-cycle engine according to the present invention will be described.

  When the piston 6 is at the bottom dead center shown in FIG. 1, combustion gas is discharged from the exhaust port 24 and scavenged by the air-fuel mixture, as will be described in detail later, and the cylinder chamber 8 is mixed with the air-fuel mixture. Filled with. Next, when the piston 6 rises from the bottom dead center, the exhaust port 24 and the scavenging port 22 provided on the inner surface 2a of the cylinder 2 are closed with respect to the cylinder chamber 8 by the outer surface 6a of the piston 6. The Further, the air-fuel mixture intake port 18 and the air intake port 30 provided on the inner surface 2 a of the cylinder 2 are also closed with respect to the crank chamber 10 by the outer surface 6 a of the piston 6. Accordingly, the pressure inside the crank chamber 10, the scavenging passage 20 and the communication passage 28 decreases due to the rise of the piston 6. Further, in the cylinder chamber 8, a compression process for compressing the air-fuel mixture is started.

  Thereafter, when the piston 6 rises to the position shown in FIG. 4, the air intake port 30 provided on the inner surface 2 a of the cylinder 2 and the communication passage 28 provided on the outer surface 6 a of the piston 6. The two ports 36 gradually overlap, and the air intake port 30 and the second port 36 communicate with each other. Since the internal pressure of the communication path 28 is reduced, air flows into the communication path 28 from the air intake port 30, thereby mixing the air flowing into the communication path 28 and the communication path 28. The air is mixed with each other and the air-fuel mixture in the communication passage 28 is diluted (hereinafter, the diluted air-fuel mixture is referred to as “lean air-fuel mixture”, and the original air-fuel mixture is referred to as “normal air-fuel mixture”). A lean air / fuel mixture that is leaner than the normal air / fuel mixture is formed. Simultaneously with the overlap of the air intake port 30 and the second port 36, the scavenging port 22 provided on the inner surface 2 a of the cylinder 2 and the communication passage 28 provided on the outer surface 6 a of the piston 6. The first port 34 gradually overlaps, and the scavenging port 22 and the first port 34 communicate with each other. As a result, the lean air-fuel mixture flows from the communication passage 28 through the scavenging port 22 into the scavenging passage 20. The exhaust port 24 and the air-fuel mixture intake port 18 provided on the outer surface 2 a of the cylinder 2 remain closed by the outer surface 6 a of the piston 6.

  Next, when the piston 6 rises to the position shown in FIG. 5, the air intake port 30 provided on the inner surface 2 a of the cylinder 2 is moved to the second port 36 of the communication passage 28 by the outer surface 6 a of the piston 6. Closed. Thereafter, the scavenging port 22 is closed with respect to the first port 34 by the outer surface 6 a of the piston 6. At this point, a lean air-fuel mixture is present at least in the upper part of the scavenging passage 20.

  Thus, at least a period from the start of communication between the air intake port 30 and the second port 36 to the closing by the outer surface 6a of the piston 6 moving from the bottom dead center to the top dead center, the communication path. 28 remains in communication with the scavenging port 22.

  Further, at the position shown in FIG. 5, the air-fuel mixture intake port 18 provided on the inner surface 2 a of the cylinder 2 is opened to the crank chamber 10 by the outer surface 6 a of the piston 6. Thereby, the air-fuel mixture intake process is started, and the air-fuel mixture flows into the crank chamber 10.

  Further, the outer surface 6a of the piston 6 closes the exhaust port 24 and the scavenging port 22 with respect to the crank chamber 10 and the mixing for a certain period while the piston 6 moves from the bottom dead center to the top dead center. By opening the air intake port 18 to the crank chamber, the air-fuel mixture is sucked into the crank chamber 10 from the air mixture intake port 18.

  When the piston 6 rises to the top dead center shown in FIG. 6, the compression process in the cylinder chamber 8 and the air-fuel mixture intake process in the crank chamber 10 are finished. The air-fuel mixture in the combustion chamber 8b is ignited by the plug 15, the air-fuel mixture burns, and the combustion gas expands. In FIG. 6, the air intake port 30 is open to the crank chamber 10, but since the air-fuel mixture intake process has ended, that is, the pressure in the crank chamber 10 has increased, It does not flow into the crank chamber 10. If comprised in this way, the dimension of the said 2 cycle engine 1 can be made small.

  While the piston 6 is lowered to the bottom dead center shown in FIG. 1, the exhaust port 24 is gradually opened to the cylinder chamber 8, and the exhaust process is started. Combustion gas (exhaust gas) is discharged from the exhaust port 24. Further, the air intake port 30 and the air-fuel mixture intake port 18 are closed with respect to the crank chamber 10 by the outer surface 6a of the piston 6, and the pressure in the crank chamber 10 is increased. Next, the scavenging port 22 is opened to the cylinder chamber 8 by the outer surface 6 a of the piston 6. Thus, the scavenging process is started.

  Since a lean air-fuel mixture exists at least in the upper part of the scavenging passage 20, when the scavenging port 22 is opened to the cylinder chamber 8, the lean air-fuel mixture first flows into the cylinder chamber 8, Thereafter, a normal air-fuel mixture flows into the cylinder chamber 8.

  Even if the lean air-fuel mixture blows out from the exhaust port 24, since the air-fuel mixture is lean, the amount of unburned fuel (fuel) discharged is reduced compared to the case where the normal air-fuel mixture blows out from the exhaust port 24. can do.

  Further, even if the lean air-fuel mixture remains locally in the cylinder chamber 8, and hence in the combustion chamber 8b, the lean air-fuel mixture containing fuel does not hinder ignition, so that an air layer not containing fuel does not enter the combustion chamber 8b. Unlike the case where it remains locally, the air-fuel mixture in the combustion chamber 8b is reliably ignited and combustion is performed.

  When comparing the present invention with a stratified scavenging two-cycle engine, the stratified scavenging two-cycle engine is set to give priority to not discharging unburned fuel. The air layer introduced into the cylinder chamber 8 may remain locally in the combustion chamber 8b to prevent ignition. The stratified scavenging two-cycle engine is intended to scavenge by sending a sufficient amount of air into the cylinder chamber 8, and accordingly, the amount of air-fuel mixture sucked from the air-fuel mixture intake port 18 is increased accordingly. In some cases, it is necessary to increase the concentration, and it becomes difficult to adjust the vaporizer, or it becomes difficult to adjust the vaporizer due to the sensitivity of the vaporizer to changes in environmental factors.

  On the other hand, in the two-cycle engine according to the present invention, as described above, even when the lean mixture is blown through, the amount of unburned fuel can be reduced, and the lean mixture becomes the combustion chamber. Even if it remains locally in 8b, stable output and acceleration can be obtained without impeding ignition of the air-fuel mixture in the combustion chamber 8b. In addition, since the appropriate range of the carburetor for fluctuations in environmental factors can be secured, the output of the two-cycle engine can be maximized under various environmental conditions.

Further, since the communication passage 28 of the piston 6 opens into the crank chamber 10, a stratified scavenging two-cycle engine having a piston communication passage that is not connected to the cylinder chamber and the crank chamber over the entire stroke of the piston. As a result, the piston length can be shortened, and as a result, the engine can be prevented from being enlarged.

  A comparative experiment was conducted between a two-cycle engine according to the present invention having the same displacement (40.2 cc) and a two-cycle engine scavenging with a normal mixture (hereinafter referred to as “conventional two-cycle engine”). With respect to the total hydrocarbons per gram per hour (g), when the rotational speed was changed from 8000 rpm to 10,000 rpm under the throttle full open condition, the conventional two-cycle engine changed gently from 45 g to 34 g. In the two-cycle engine according to the invention, it gradually changed from 34 g to 24 g. Therefore, the two-cycle engine according to the present invention was able to reduce the total hydrocarbons by about 25% compared to the conventional two-cycle engine. That is, the amount of unburned fuel could be reduced.

  In addition, when the engine speed was changed from 8000 rpm to 10,000 rpm with the throttle fully open, the output (horsepower) of the conventional two-cycle engine changed gently from 1.7 horsepower to 1.9 horsepower. In the two-cycle engine according to the invention, the speed changed gently from 1.7 hp to 1.9 hp. Therefore, the two-cycle engine according to the present invention was able to exhibit the same output as the conventional two-cycle engine.

  In addition, an acceleration test was performed with a brush cutter equipped with each of the two-cycle engine according to the present invention and the stratified scavenging two-cycle engine. When the rotational speed is suddenly accelerated from 3000 rpm (idling) to 10,000 rpm (high speed rotation) (the throttle is grasped at a stroke), the two-cycle engine according to the present invention accelerates smoothly according to the opening and closing of the carburetor valve, whereas the layered scavenging The formula 2-cycle engine showed a dull acceleration. This is because, in a two-stroke engine with a stratified scavenging type, an air layer remains locally in the combustion chamber at one of the timings of a rapidly changing rotational speed to prevent ignition, or the amount of air-fuel mixture is insufficient or the lubrication effect This is probably due to the fact that combustion has become unstable.

  Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the invention described in the claims. Needless to say, these are also included within the scope of the present invention.

  The scavenging method of the two-cycle engine according to the present invention is preferably the reverse scavenging method, but may be other methods.

In the above-described embodiment, the communication path 28 is formed inside the piston 6. However, the communication path 28 may be a recess such as a groove formed on the outer surface 6a of the piston 6. .

  In the above-described embodiment, the air-fuel mixture intake port 18 is provided on the inner surface 2 a of the cylinder 2 and is opened and closed with respect to the crank chamber 10 by the outer surface 6 a of the piston 6. May be provided on the inner surface 4a of the crankcase 4 and opened and closed with respect to the crank chamber 10 by a valve (not shown).

  In the above-described embodiment, the communication passage 28 communicates with the air intake port 30 and the scavenging port 22 until after the air-fuel mixture intake port 18 is opened to the crank chamber 10. If the piston length is allowed to increase, the communication path 28 is connected to the air intake port 30 and the scavenging port 22 for a certain period before the mixture intake port 18 is opened to the crank chamber 10. You may be comprised so that it may communicate.

1 2-cycle engine 2 Cylinder 2a Inner surface 6 Piston 6a Outer surface 8 Cylinder chamber 8a Bore 10 Crank chamber 18 Mixture intake port 20 Scavenging passage 22 Scavenging port 24 Exhaust port 28 Communication passage 30 Air intake port 34 First port 36 Second port port

Claims (6)

A two-cycle engine (1),
A cylinder (2) having an inner surface (2a) constituting a bore (8a);
A piston (6) reciprocating in the bore (8a) of the cylinder (2);
A cylinder chamber (8) partitioned by the inner surface (2a) of the cylinder (2) and the piston (6);
A crank chamber (10) configured under the piston (6);
An air-fuel mixture intake port (18) for allowing a fuel-air mixture to flow into the crank chamber (10);
A scavenging port (22) provided in the inner surface (2a) of the cylinder (2) for allowing the air-fuel mixture in the crank chamber (10) to flow into the cylinder chamber (8) through the scavenging passage (20);
An exhaust port (24) provided on the inner surface (2a) of the cylinder (2) for discharging combustion gas in the cylinder chamber (8),
The piston (6) has a communication passage (28) opened to the crank chamber (10),
And an air intake port (30) provided on the inner surface (2a) of the cylinder (2) for allowing air to flow into the communication passage (28),
After the outer surface (6a) of the piston (6) moving from the bottom dead center to the top dead center closes the scavenging port (22) with respect to the cylinder chamber (8), the communication passage (28) becomes the air. The communication passage (28) is opened in the outer surface (6a) of the piston (6) so as to communicate with the intake port (18) and the scavenging port (22), thereby the air intake port (18). ) And the air-fuel mixture in the communication passage (28) form a leaner air-fuel mixture than the air-fuel mixture, and the lean air-fuel mixture becomes the scavenging port (22). Through the scavenging passageway (20),
Combustion occurs when the outer surface (6a) of the piston (6) moving from the top dead center to the bottom dead center opens the exhaust port (24) and the scavenging port (22) to the cylinder chamber (8). A two-cycle engine, wherein gas is scavenged by the lean mixture.   The outer surface (6a) of the piston (6) moving from the bottom dead center to the top dead center is after the scavenging port (22) is closed with respect to the cylinder chamber (8) and the mixture intake port ( The communication path (28) is in communication with the air intake port (18) and the scavenging port (22) for a certain period before 18) is opened to the crank chamber (10). The two-stroke engine according to claim 1, characterized in that the passage (28) opens in the outer surface (6a) of the piston (6).   The communication passage (28) communicates with the scavenging port (22) at least during a period from when communication with the air intake port (30) is started to completion with the outer surface (6a) of the piston (6). The two-cycle engine according to claim 1, wherein   The communication passage (28) is formed inside the piston (6), and has a first port (34) that opens to the scavenging port (22) and a second port that opens to the air intake port (30). The two-cycle engine according to any one of claims 1 to 3, further comprising a port (36).   The two-stroke engine according to any one of claims 1 to 3, wherein the communication path (28) is a groove formed in the outer surface (6a) of the piston (6).   The air-fuel mixture intake port (18) is provided on the inner surface (2a) of the cylinder (2), and is opened and closed with respect to the crank chamber (10) by the outer surface (6a) of the piston (6). The two-cycle engine according to any one of claims 1 to 5, wherein

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